HMV Spectre. Noise from speaker on start up.

[hayerjoe]

I have an early 70s HMV Sceptre radiogram, it's a big modular transistor system. it needed a fair bit of electrical work 6 months ago to getting it running well and it's been fine for that 6 months.

But for the last couple of days when turning it on the speakers make an unpleasant noise for about 5 seconds, sounds like the noise I've heard when another system is powered down and the capacitors just release their charge. so like an intense pop and crackle for a few seconds. after it's settled is all totally fine for hours

any ideas what's causing this?

[John_BS]

Originally Posted by hayerjoe

I have an early 70s HMV Sceptre radiogram, it's a big modular transistor system. it needed a fair bit of electrical work 6 months ago to getting it running well and it's been fine for that 6 months.

But for the last couple of days when turning it on the speakers make an unpleasant noise for about 5 seconds, sounds like the noise I've heard when another system is powered down and the capacitors just release their charge. so like an intense pop and crackle for a few seconds. after it's settled is all totally fine for hours

any ideas what's causing this?

I'd suspect a transistor: especially if this happens on all inputs? Pre /post volume control?

John

[Sideband]

Yep....I'd suspect a transistor as well. I had an old Akai amp that used to do similar when switched on or off. It turned out to be one of the pre-amp transistors. I replaced it with a BC something or other and it was fine. Sometime later the same thing happened on the other channel.....it was the same fault. I subsequently read that the transistors developed corrosion on their leads and this would work its way past the seal and into the transistor itself.

If your HMV has the notorious 'lockfit' transistors fitted (like BC147/148/157/158 etc) these are known to give similar problems.

[hayerjoe]

thanks John and Sideband. I will extract the chassis and look at those transistors, these HMVs are covered in the BC transistors. And as I said it needed a lot of work 6 months ago, was running way too hot, bias all wrong, many resistors high etc, so it would be no surprise that the transistors had been stressed as well. I shall report back

[Sideband]

If it's got Lockfits (those black not quite triangular things) then treat them with suspicion. I had an old Philips scope that was full of the things and it spent more time with the covers off than in use....until I changed them all!

Just as a point of interest, if it does have lockfits and you have say BC147, 148 etc you can replace them with BC547, 548 etc which don't suffer from the same problem.

[hayerjoe]

well the mere suggestion that I was planning to rummage through its nethers seems to have fixed it! I hate intermittent faults, but try as I may I cannot get it to do it again

I had not plugged it in for about 4 weeks, and it had been in a cold but definitely not damp room, before I brought it back up to the lounge room. Is it possible being moved upset it (unlikely, it's not valve based)? I noticed that the speaker plug on the offending channel was not well pushed together, could that have caused it?

I'm clearly clutching at straws now!

[John_BS]

I was planning to rummage through its nethers

That sort of innuendo is deprecated on this site!



Sounds like a good wiggle of all connectors etc might be the solution - perhaps aided by a light application of switch-cleaner.

J

[Diabolical Artificer]

Can someone post a picture of a "lockfit" transistor please? Despite searching online I can't find a definitive ID.

Andy.

[vidjoman]

Just googled and got 100’s of images.

[Diabolical Artificer]

Just googled and got 100’s of images.

I've searched in the past for a quick definitive picture & definition. Don't use G**gle, but did just manage to find an image. See attached for other simpletons like myself.

Andy.